1. Field of Invention
The present invention concerns the placing of tubes in underground ducts. In many already installed underground ducts, be they of metal or of synthetic material, it may be necessary to place one or several tubes, generally of a synthetic material, obviously having cross sections smaller than that of the ducts already installed. These tubes are destined for multiple uses, as for example for subsequently receiving an optical cable.
2. Description of Related Art
Various processes have been developed for placing such a tube in an already installed duct, which can already contain one or several other elements, such as cables or other conduits.
The work titled xe2x80x9cInstallation of Optical Cables in Ductsxe2x80x9d by W. Griffioen, published by CIP-Gegevens Koninklijke Bibliotheek, Den Haag, (year), ISBN 90-72125-37-1, describes in detail notably a laying process by blowing.
It is also known that when a tube is subjected to a difference of pressure between the pressure surrounding it and that residing inside the tube, this tube resists better mechanically when the pressure inside the tube is superior to that surrounding it. In other words, a tube able to resist a determined internal superpressure is susceptible to deteriorate when this same value of superpressure is applied from the outside towards the inside of the tube.
As in the aforementioned laying process, a situation occurs where the external pressure of the tube is superior to its internal pressure, there can be risks of deformation and/or rupture of the tube depending on the pressure used at the inlet of the system and on the length of laying.
A first purpose of the invention is thus to propose a laying process that avoids this kind of disadvantages.
A second purpose of the invention is to propose a device that will avoid this kind of disadvantages when laying a tube in a duct.
The first aim is achieved by a process such as described in claim 1, whereas the second aim is achieved by a device as described in claim 6. The dependent claims concern particular embodiments or variants of the process or device according to the invention.
Two particular embodiments of a process and the corresponding devices according to the invention are described hereafter, this description making reference to the attached drawing comprising the figures.